In this image, the warmer (and lower) clouds are yellow. The cooler
(and higher) clouds are white.

The clouds in this image are aligned
along a strong but very slow moving cold
front trailing toward the southwest from a
low pressure center located
over north central Missouri. To the south of this cold front is a mass of
warm air from the Gulf of Mexico. This warm air is very moist with
dew points of about 70 F. To the north of
this cold front is a mass of cool dryer air from Canada. Where the warm
moist air is pushed above this cool dryer air, clouds form. The
convergence of these
air masses along the front results in lifting and a
cyclonic circulation at the surface.

The image shows
numerous cumulonimbus clouds developing along and on
the southeastern
side of the cold front. Some of these clouds have tops up to 50,000 ft.
The air is very
unstable with the 00~UTC
sounding from Little Rock, AR, indicating a
CAPE
of around 2500 J/kg and the 00~UTC sounding from Ft.\ Worth, TX, giving a
CAPE of more than 3000 J/kg.
A southerly
low-level jet of 50 knot winds from the
Gulf of Mexico provides sufficient wind
shear for the development of
severe thunderstorms. These thunderstorms
are part of a large
MCS
located just ahead of the cold front and approaching the
Arkansas-Louisiana-Texas border.
The National Weather Service issued a tornado watch for southeast
Oklahoma, northeast Texas, and western and central Arkansas at 1645 UTC.

This line of clouds produced severe thunderstorms with heavy rain.
Parts of northwest
Arkansas received 3-6 inches of rainfall. Rainfall rates of 1-2 inches
per hour were measured by
Doppler radar in some areas.
Flash flood warnings were issude for central and northeast Oklahoma,
Arkansas, and southwest Missouri. Radar showed several persistent
mesocyclones and brief
tornadoes were reported in Texas. One
inch hail and three tornadoes were reported in Arkansas.

Note the cloud shadows. From the date and time and the length of a
shadow, you should be able to estimate the height of the cloud.